For years the public has been bombarded with the statement "Pay me now, or pay me later", and the vision of a well-fed auto mechanic leaning over a suffering automobile engine smiling benignly into the camera holding an oil filter. These filters are well-known and the cartridge inside is held together in its oil-filtering relationship by end caps, which allow entry of the oil to the interior of the filter to be forced through the filtering medium to remove harmful grit and dirt for return to the operating internal combustion engine. Alternative materials for the preparation of all parts of an oil filter have been a continuing quest in the search of excellence in performance and for a reduction in cost. This invention relates to the molded end caps and the preparation of such with a special polyetherpolyurethane material.
Several uses of a specific thermoset polyetherpolyurethane system is described in U.S. Pat. No. 5,001,167 where many other attempts to use polyurethanes in the presence of hydrocarbon fuels, hydrocarbon lubricants, freezing point depressant fluids (antifreeze), and water are described. This patent also describes prior art attempts to prepare solvent resistant polyetherpolyurethane products and offers its solution, specifically mentioning an operation relating to oil filters and the end caps for such filters. The solution proposed related to the well-know polyether polyol component for the preparation of a thermoset polyurethane elastomer. The polyether polyol proposed in the prior art U.S. Pat. No. 5,001,167 contains at least 50 wt % oxyethylene groups, based on the total active hydrogen component, but which does not involve the well-known concept of using "ethylene-oxide capped" polyols. Said another way, the polyether polyol contains considerable oxyethylene units but the reactive terminal groups are all secondary hydroxyl groups produced by the reaction of an epoxide containing three or more carbon atoms. As taught by U.S. Pat. No. 5,001,167, polyurethanes prepared from polyether polyols are more resistant to hydrolysis in the presence of water than are polyester polyols frequently used in the production of polyurethane products.
However, the polyether polyol reaction material taught by U.S. Pat. No. 5,001,167 has its drawbacks since the oxyethylene units are more susceptible to the absorption of water, which if present during the urethane forming reaction, reacts with isocyanate groups to produce carbon dioxide which causes foaming. Foam forming reactions cause a deterioration in the physical properties of solid polyurethane products, thus making them more likely to fail in a high temperature, high pressure environment in the presence of a combination of aggressive solvents.
Not only must an end cap for an oil filter have resistivity to a number of aggressive solvents in a hostile environment where temperature, pressures, and contaminants abound, they must have physical properties which do not lead to product failure over long periods of time of exposure to this hostile environment. The product must be hard, but it cannot be so hard that it becomes susceptible to cracking upon standing. It must have sufficient tensile strength over a wide range such that it can stand the internal pressures of the operating internal combustion engine. Even though polyether polyols themselves prepared only from epoxides having three or more carbon atoms are well known, this invention is the discovery that specific combinations of these polyether polyols, when reacted with the well-known methylene bridged aromatic polyisocyanates having a functionality greater than 2, an oil filter end cap having outstanding physical properties as well and resistance to solvents, regardless of whether hydrocarbon, water or glycols, results. Previously, polyurethane formulations used for this purpose suffered from the disadvantage of lacking one or more of the physical properties or as set forth above in connection with the discussion of this prior art patent. Further polyurethane thermoset polymer described in the prior art have shown a tendency to crack, particularly radial cracks which form upon allowing the part to sit on the shelf. Replacement oil filters must have a good shelf life without deterioration.
These disadvantages, as well as other inferior physical properties resulting from the use of the polyether polyols containing oxyethylene groups, are avoided by using a particular polyether polyol combination in the polyurethane elastomer forming the oil filter end cap of this invention.